There are varying degrees of quality when it comes to TEFL/ESL certificates and courses. When it comes to TEFL Accreditation you can find a course that is accredited and audited by a recognized external body, like ours, or you can find one that is unaccredited and try your luck.
To start up an English teaching course and give out TEFL certificates, you theoretically need no training or experience. You could start a course yourself right now and start handing out TEFL certificates.
Hence, the organization you use to do your course can carry a lot of weight with ESL academies and other potential employers. Accreditation means your course is valid and teaches what it should. This is even more important if you want to use your TEFL certificate in another city or country where your TEFL school is unknown.